It is known that steam can be used to facilitate the manufacture of textile materials, e.g., fibers, yarns, filaments, tows, and fabrics. See U.S. Pat. Nos. 3,452,132; 4,639,347; 4,704,329; and the other references mentioned below, each of which is incorporated herein by reference. In general, steam treatments are used, for example, to facilitate drawing, annealing, heat setting, and/or relaxing of the textile materials. Steam treatments are also used during application of certain dyes and chemicals to textile materials, as disclosed, for example, in U.S. Pat. Nos. 3,349,578 and 3,889,495. To simplify the discussion here, the textile material described below will be a filament yarn or tow, it being understood that the apparatus and processes, set forth below, can be applied equally to other textile materials, e.g. woven or knit fabrics, which require steam treatment.
Steam treatment is the application of steam to the textile material so that heat from the steam is imparted to the material. (Steam treatment may be used to also impart heat to a dye or other chemical product being applied to a textile material and the apparatus and methods of this invention may be used in such a treatment. However, the present disclosure will focus on the steam treatment of textile material, itself.) This treatment is typically conducted in an enclosure, a steam chest. The chest has a steam inlet and two apertures through which the continuous textile material may pass, i.e. a material inlet and a material outlet. Typically, these apertures are shaped as long, narrow slits to accommodate sheet-like material, with the long dimension (length) of the aperture being in the direction of the width of said sheet-like material and the width of the aperture being in the direction of the thickness of said sheet-like material. Inside the chest, the steam comes in contact with the material and heat is transferred to the material. The heat available for transfer comes, primarily, from the condensation of the steam, and the material will acquire heat until it comes to equilibrium with the condensation temperature of the steam. So, if the process requires the material to be heated to 100° C., then steam at atmospheric pressure may be used. To attain higher temperatures, one may either use superheated steam or pressurize the chest to increase the condensation temperature. The latter is preferred. So, if the process requires a temperature of 150° C., then steam at about 476, kPa (or 54, psig) may be used.
The efficiency of the steam chest is determined by the amount of steam needed to heat the material. In practice, not all the steam entering the chest is used to heat the material because of leakage at the apertures. This leakage becomes greater as the steam pressure (i.e., the condensation temperatures) increases, so efficiency will decrease. One way of reducing leakage would be to decrease the width of the aperture, but the practical limit is that the moving material cannot contact the stationary surfaces of the aperture because of the risk of abrasion or snagging. Moreover, the material undergoes considerable vibration due to turbulence and high velocity steam escaping through the aperture. With a clearance of at least one (1) millimeter above and below the material and a pressure of about 500, kPa one could expect a steam leakage rate in excess of 50, kg of steam per hour per centimeter length of aperture. A typical commercial textile tow processing rate is about 50, kg of tow per hour per centimeter length of aperture. Accordingly, the steam leakage rate is nearly equal to the processing rate. But only about 10% of that steam is needed to heat that material to the steam condensation temperature. Therefore, this process is only about 10% efficient.
Several solutions to this leakage problem have been suggested. These solutions may be grouped into three categories. Those categories include labyrinth seals, nip roll seals, and sonic seals.
Labyrinth seals are set forth in U.S. Pat. Nos. 3,349,578; 4,332,151; 5,287,606; and Japanese Unexamined Patent Publications (Kokais) Nos. 5-33237; 5-44132; 5-339839; 6-93554; 6-57573; and 8-246330. For example, in U.S. Pat. No. 4,332,151, labyrinth seals are illustrated as tubes having a plurality of apertures through which yarn is passed into and out of the steam chest. Also see, Japanese Kokai 6-57573, labyrinth seals enclose nozzles at ends of the steam chest. Yarn may be abraded, snagged, or damaged by contact with elements of this seal, so sufficient clearance must be provided to accommodate the yarn's vibration. In the foregoing example, the clearances lead to high steam losses which can only be prevented with very long seals with a large number of chambers. Such seals are costly and lead to alignment problems.
Nip roll seals are illustrated in U.S. Pat. Nos. 3,808,845; 4,064,582; 4,111,434; 4,087,992; 4,064,713; 4,089,194; 4,184,346; and 4,949,558. For example, in U.S. Pat. No. 4,111,434, a nip roll seal mechanism is installed at the feed and takeout apertures of the steam chest. Rollers are intended to block the escape of steam from a passage which is in communication with the steam chest. The seal is formed by the nip between the rollers through which the tow passes. To minimize steam loss, the nip roll pressure must be higher than the steam pressure, and this can be a source of fiber fusion and damage.
Sonic seals are illustrated in German Patent Specification DE19546783Cl and U.S. patent application Ser. No. 09/334,140, filed Jun. 15, 1999, of Reese and Goodall. In German Patent DE19546783Cl, the device consists of an upstream jet, an injector jet, a treatment channel with no entry and exit seals, but instead three constriction zones. In operation, this arrangement of elements acts to seal the device from steam loss by developing a stationary shock wave that reduces pressure at the aperture. Such seals are useful for small scale, but are not practical for commercial lines because both capital costs and operating costs are high or prohibitive.
In view of the foregoing, there is still a need for a simple, low cost sealing mechanism which will increase efficiency and reduce noise.